1. Field of the Invention
The present invention relates to an ink jet printing apparatus including a plurality of nozzle arrays each having a plurality of nozzles which are arranged in a direction crossing a direction in which print media are conveyed and through which ink droplets are ejected so that the nozzle arrays are used to sequentially print rasters. The present invention also relates to a relevant ink jet printing method.
2. Description of the Related Art
A printing apparatus using an methodink jet method of ejecting ink droplets through a plurality of nozzles formed in a print head is commonly used not only as a printing apparatus but also in various instruments. This printing apparatus drives ejection energy generating elements provided in the nozzles in the print head to eject ink droplets. Known ejection energy generating elements include electrothermal converting elements such as heaters and electromechanical converting elements such as piezo elements. All these elements are driven by applying electric signals (driving pulses) corresponding to print data to the elements, to eject ink droplets through the nozzles. For example, a printing apparatus using electrothermal converting elements applies a driving pulse to the electrothermal converting elements to generate thermal energy so that the thermal energy subjects ink in the nozzles to film boiling to generate bubbles. Pressure resulting from the generation of the bubbles allows ink droplets to be ejected through the nozzles.
Some of these printing apparatuses are what is called full-line printing apparatuses that perform printing using print heads (also referred to as lines heads) including long nozzle arrays each having a large number of nozzles collectively arranged over a range equal to or greater than the width of print media used. The full line printing apparatus allows each of the line heads to simultaneously form a single raster line, and is thus suitable for high-speed printing. As a printing apparatus using line heads, Japanese Patent Laid-Open No. 2005-238556 discloses a printing apparatus having a plurality of full line heads ejecting ink of the same color and arranged along a direction in which print media are conveyed.
The printing apparatus disclosed in Japanese Patent Laid-Open No. 2005-238556 uses data on an image of the same color to form the image so that the line heads sequentially form the respective rasters. The printing apparatus can print the image faster than printing apparatuses using a single full line head. Furthermore, this printing apparatus adopts a divided image method in which in forming a single image, the different print heads are responsible for the respective rasters for printing. Thus, even if any nozzle becomes defective, that is, ink cannot be normally ejected through the nozzle owing to, for example, contaminants attached thereto, the divided image method enables a reduction in the adverse effects of the defective nozzle on print quality. That is, dots preceding and succeeding (in a column direction) an area in which a dot is to be formed by the defective nozzle are printed by nozzles in another print head. This enables a reduction in the adverse effects of the defective nozzle compared to the case in which each column is always printed by the same nozzle.
However, two or more nozzles in each of the adjacent print heads which are responsible for the same column may all become defective. In this case, two or more consecutive areas in which the dots are otherwise formed are blank. Then, the print quality may be significantly degraded.
In contrast, it is possible to allow the area that is otherwise printed by the defective nozzles to be printed by nozzles in another print head which are responsible for the same column as that for which the defective nozzles are responsible, in order to complement the printing of the area. However, in this case, to increase the frequency with which the appropriate nozzle array is used, it is necessary to set a longer driving period for the nozzle array. As a result, high-speed printing performance, which is characteristic of the divided printing method, is not sufficiently achieved.